A conventional piezoelectric transformer driving device that is used for an electrographic image forming device is disclosed in Japanese laid-open patent application publication number H11-206113. In this device, a piezoelectric transformer that generates a high voltage with a low voltage input by using a resonance phenomenon of a piezoelectric vibrator is controlled by an output signal of a voltage-controlled oscillator (VCO) to output the high voltage.
However, because the device with the structures discussed above is configured with an analog circuit, such as a VCO, there is a problem of having a large number of parts. There is also the additional problem that it is hard to have both a high voltage output near resonance frequency and a short rise time for the output voltage.